This will be the thread for the contrapteur mini-cnc project.
The goal is to make a complete replica of the mini-cnc, but using metric parts.
The good thing about the mini-cnc is that it uses all contraptor parts, so translating it's part is basically translating contraptor.

So to start, we need a frame with about the same dimensions as the contraptor mini-cnc.
Here bellow is a draft, conversion has been made the following way :

For short parts, use parts with the same number of holes.

For long parts, use parts about the same length.

Picture :

It ends up looking very much alike.
Some things may need to be changed once we start adding the moving parts, we'll see then.

One thing I would suggest is cutting these shapes out and checking how well they work. For example, the stack of plexi may slightly rotate and skew - I had this happen when trying to come up with lasercut replacements for metal Contraptor parts. It can help if you have access to/nearby friend with a laser cutter.

No lasercutter around here, this town really misses a hackerspace.
I'll have them made at ponoko, if there's a problem I'll have them made again, etc … expensive but it's the only option until the birth of the contraptor laser-cutter ^^

Also, I'll soon have a reprap, so it will be possible to test 3d-printed parts.

None of these two options are possible for DIY, so I still need to design metric replicas of the DIY-able contraptor equivalents.

About the rotate/skew, it's my main fear with the lasercut option. My current assumption is that problems can be avoided by securing the bolts very very tightly. But this needs testing. Another option would be to add a drop of glue between every layer before vising, but that's not a very clean option.

Couple of other things to keep in mind is the stated thickness of acrylic may often be inaccurate. For example some 1/4" acrylic I got was actually 7/32". Another problem was that when laser cuts through the material, the resulting cut has a bit of a slant to it. I'm not sure if it depends on how well the laser cutter is set up. I think the slanted edge should not be a problem in these designs though, but the thickness may be.

Ouch for thickness !
That will need testing as always, but it's nice to see problems before they may happen. Same thing for slant.
Most of the lasercut designs should work anyway if the error is kept small.
Also I'll be changing some 2mm thick parts to 4mm thick designs, that should help ( and reduce cost too ).

The motor mounts are now lasercut parts, this is mostly for simplification and price reduction.

All of the axes now use the sliding element. It is a new version of it, with a single length : 40mm, and all the inside covered with UHMW-PE. Hopefully it is also a more simple version, but it needs testing.

The table is elevated by 20mm, it will be put on 4 adjustable rubber+screw+screw-handles-things, for super easy adjustment of the table ( up to about 1 or 2mm ) . The screws will be in a place where they do not stick out of the table ( by using 2 tables of 4m thickness on top of each other ) , so 100% of the table area will be usefull. Also needs testing.

All of this gives a bigger working area : 320x220 mm ( more than A4, yeee ! ).

The version on the right is for use with UHMW-PE extrusion, the whole element is coated with plastic, and the angle is in contact with the element on all the surface. It needs to be extruded, so it's suitable for mass-production, but difficult for DIY. It may also be 3D-printable.
The version on the left is closer to the original. It uses two UHMW-PE pads ( instead of 6 ) but works similarly. It can be made with the contraptor mini-cnc and a dremel, that's what was tried here :

The material is a cutting table from the mall, it's the only UHMW-PE that could be found locally ( EDIT : in fact not UHMW-PE, probably just HDPE, does not slide as well ). It was 9mm thick, close enough to the 10mm in the design.
Here is how it looked in Cambam :

A note on cutting UHMW-PE : It was difficult to find a bit to cut it with, finally ended up with one with a teethed ball at the end.
Cutting too much at a time ( DepthIncrement, used 0.25 ), too fast ( CutFeedrate, used 250 ) or cutting only one track ( used 3 ) led to plastic accumulating in the tracks, then after a while melting and causing chaos.
Could probably be solved by using some sort of fan/extractor.

After running in about every mechanical/software problem you can have, two days later, here is the first successful cut :

It fits in the metal tube ( think it's steel, there was no aluminium at the hardware store ) :

And the angle fits in it :

It fits, but in that state ( closed square ), it would be difficult to adjust ( too stiff, no bending ).
After playing with it, here is what seems to work best :

This way it slides well, and the angle is held well, and it would be adjustable with screws.

There is another board with 16 failed attempts, preferred not taking a picture, it's not glorious :)

Problems :

Mis-adjusted axes.

Bolts/nuts that fall

Endstops that fail ( currently made out of cardboard and glue … )

350mm speed not suitable when milling

Current setting not suitable when milling

Broke the circles when fixing the microstepping problem, took quite some time to find a fix.

As you can see, it's all mostly related to me being sloppy. If I am to blame anything else than me, it'd be the hole size/bolt size in contraptor, really the biggest problem to me. Very related to that is also the difficult adjustment of the linear stages' ball bearings. Probably a lesser problem to more accurate/methodic people.

Another update : Drilled a second one today : it definitely does not slide as well as the UHMWPE from the contraptor parts … after looking for long at it : it's very probably not UHMW-PE, probably something close …
Now looking for cheap UHMWPE or PTFE to order from Europe ( or from china when the holliday is over there ).

Thank a lot ! Will be contacting these.
Currently in contact with a provider in the UK, the order may be going soon … also they have PTFE, which I'd like to try out for this job.

Also, anyone has experience with bending UHMW-PE or PTFE ?
The idea would be to take a 40x100x3mm sheet, and bend it into the "open square tube" shape that's needed. I remember doing some plastic bending at school, using hot air, that's a nice coincidence : I just received my hot air SMD station.
I'll try it anyways, but if you have advice …

UHMWPE 10mm and 20mm ( it's actually called RG1000, but they say it has the same caracteristics at a lower price ) :

First thing made was the UHMWPE parts for the sliding elements, cut from the 20mm sheet … that went well :

Result : they fit the angle perfectly, and they slide very very very very well. Very impressive. Next step for this element is to make the aluminium part ( cut/drill the square tube ).
The very good thing with cutting UHMWPE is that it does not melt easily the way the other plastics tried do, makes everything easier.

Second thing are the lead nut holders. They are supposed to be made with a lasercutter, but they can also be made on the mini-cnc … it just takes a lot more time and noise.
Not finished on that, it's very difficult to find the right settings, as the polypropylene melts very easily, but here is a picture of so far :

The cut with 3 parts at the bottom went well, the parts fit nicely.
At the top it is cutting all the parts for a complete nut holder at the same time. That second cut went bad shortly after the picture due to melting causing missed steps missing more melting …

That's all for this time, I'm away on a trip for a week, more melted plastics after that :)

Not much time now, I'll take the pictures when back from the trip, but for now :

Cutting UHMWPE : RPM setting about 5, the bit is a 2.2mm "teethed cylinder", it did not come with the Dremel, the feedrate is 200mm and the depth/pass is 0.5mm.

Cutting polypropylene : no successfull pass yet, the closer I got was with : RPM setting minimal ( any faster it melts the ejected plastic powder ), 1.2mm "diamond sphere" bit, not Dremel again, feedrate is 150mm, depth/pass is 0.08mm ( any more and it melts ). Even with that configuration, it starts melting when finishing the last pass. But I'll probably get it right next time.

Not much time for working on this now, and probably for all march.
The Polypropylene melts too easily to correctly drill the parts in it. Just ordered acrylic sheets ( pre-cut to 150x200mm, will make things easier ). Also a few other plastic types to try including HDPE.

Tried replacing in the design another metal part from the contraptor mini-cnc, with one that can be made on a lasercutter or on the mini-cnc itself : the dremel mount.

Not much to say, just a picture :

This should also work on the contraptor mini-cnc, so as the contrapteur mini-cnc does not exist yet, I'll maybe try it on the current machine first.
A definitive version will probably have more rounded angles.

Received the lasercutter, had to change like half of the parts, including all of the electronics, but since a few days I'm able to make cuts that are close to correct.
It's controlled by grbl, so it works fine with GCODE generated by cambam for the mini-cnc, with just a few little adjustments.

About grbl, to get the lasercutter to work, I had to fix a bug in it, in the process I had to read it's code several times : it's awesome ! It really should be contraptor's "official" firmware.

The hexagonal shapes are what holds the lead nut ( M6, 18mm long ).
The "screw head" shapes at the bottom of the parts are what hold prisoner the heads of the M5 screws. These are used to attach the finished element to the rest of the contraption.
The circle shapes are what "begin" and "end" the stack of parts. They maintain both the lead nut and the M5 screws "trapped".
Finally the 4 holes in each part are for 25mm M2 screws, that hold all of the stack together.

Here is how it looks fresh out of the lasercutter :

It's still attached to the acrylic sheet with "holding tabs" :

They easily "snap" out by breaking the holding tabs, and then need just a little bit of cleanup :

Then we stack the hexagonal parts around the lead nut :

Then the two M5 screws "slide" in :

Now the two "closing" parts are used to close the stack, trap the lead nut and the two 5m screws, and the M2 screws are used to hold it all together :

It can then be attached to a contraption and move around a M6 leadscrew :

In the end, it seems to work good. I can't wait to use it for real in the mini-cnc.

You can see the "official" pictures on the ebay page here. It was about 800$ shipping included.
I had to hack it a lot, the hardware and software that comes with it are worth absolutely nothing, I was not even able to use it for simple tasks.
But in the end, there was nothing difficult if you have the basic mini-cnc knowledge.

Here's how it looks like now in my office :

For the electronics, I simply took those of the mini-cnc, added the pwm control for the laser tube, and removed the endstops ( I how not yet figured out how they are wired inside the machine, plus it does not break the machine when you go too far, it just makes a lot of noise ).
So it's an arduino uno, and two pololu drivers.

Inside the machine, the only thing that is still used is the power supply for the laser.
There is an unused connector to an opto-isolator that controls the laser, on that board, so it can be used for pwm control, very nice.
All the rest is bypassed and connected to the arduino outside :

The optics :

In the end, once you have played with it a bit, the lasercutter is a much less frightening thing than it was. I have a spare lasertube, and spare optics, so all I need now is a laser PSU, and I'll be working on a contrapteur lasercutter ! ( well I need to do the mini-cnc first ).